Electrolytic condenser



May 27 1941;

w. DUBlLlER ELECTROLYTIC CONDENSER Filed Nov. 5, 1937 2 Sheets-Sheet lmmmlim H I \\R INVENTOR. w'llliam Dubnlur W/MLPUC.

ATTORNEYS.

E PLEAT DEPTH IN INCHES May 27, 1941; w. DUBILIER 2,243,814

ELECTROLYTI C CONDENSER Filed Nov. 5, 1937 2 Sheets-Sheet 2 3 I J8 l l ll Fig 5 o l l l k ANODE LENGTH IN INCHES INVENT OR. 171 7 'llhlliam,Dubilier ATTORNEYS.

Patented May 27, 1941 ELECTROLYTIC CONDENSER William Dubilier, NewRochelle, N. Y., assignor to Cornell-Dubilier Electric Corporation,South Plainfield, N. J a corporation of Delaware Application November 5,1937, Serial No. 173,025

6 Claims.

This invention relates to electrolytic condensers of the type having alarge area of anode surface in a small space, and more particularly butnot exclusively to such condensers having a tubular metal container thewalls of which serve as a cathode.

Heretofore it has been proposed to fold, corrugate or crimp strip-likeor tubular anodes and also to provide rod-like anodes with projectingfins or geometric designs in order to increase the anode area in a givenspace. It has further been proposed to etch, emboss, or roughen theanode, thus increasing the effective area and thereby obtain morecapacity in a. given container or can. Prior anode structures havingcorrugations or the like, can be divided into two classes. In the firstclass the corrugations are open and their depth is comparable with thespaces between adjacent corrugations. This results in only a moderateincrease in anode area and capacity. In the second class thecorrugations are close, that is, the spaces therebetween are smallrelative to the depth of the corrugations.

While anodes of the second class may provide several times the area ofanodes of the first class, I have found that the close or deepcorrugations proposed heretofore have the serious defect of increasingthe equivalent series resistance of the condenser and thereby increasingits electrical losses. tice, the sides of a deep corrugation tend to bowaway from each other near the apex of the fold and to close up the openspace opposite the apex of the fold, thereby forming a bottle neck. Therelatively small, narrow cross-section of electrolyte in such bottleneck oifers a high resistance to the condenser current and inasmuch aselectrolyte resistance is an important factor in the equivalent seriesresistance of a condenser, such resistance is unduly increased.

The equivalent series resistance or power factor of an electrolyticcondenser is made up of three factors, namely, the resistance or losseswithin the dielectric film, the contact resistance of the electrolyte tothe cathode, and the electrical resistance of the electrolyte. Thedielectric film is composed of a thin layer of anhydrous and hydratedmetal salts in intimate surface contact with the anode. It has beenfound that the resistance or dielectric losses within this metal saltlayer are very small and the phase angle difference of the condenser dueto such dielectric losses is only a small fraction of a degree (abouttwo or three minutes). The second factor, or cathode-to-electrolytecontact resist- 2 A cause for such defect is that, in pracance or loss,has been found to be reasonably small and the phase angle difference ofthe condenser due thereto may be of the order of one degree or less, andcan be reduced materially by using suitable cathode metals, such ascopper, nickel, chromium or other non-filming metal. The third factor,or electrical resistance of the electrolyte, gives rise to much greaterphase angle difierences than the first two factors combined, suchdliferences being about five to nine degrees for electrolytes adaptedfor operation at several hundred volts. Hence the electrolyte resistanceis the determining factor and a low resistance path through theelectrolyte will result in a low phase angle difference andcorrespondingly low equivalent series resistance in the condenser. Thisbecomes increasingly important in condensers for higher operatingvoltages because such condensers require electrolytes of relatively highresistivity. For instance, the electrolyte for a 450-volt condenser mayhave a resistivity of about 550 ohms per cm. cube; for a 475-voltcondenser the resistivity may be about 700 ohms per cm. cube; and for a500-volt condenser it may be about 950 ohms per cm. cube; all saidresistivities being measured under the same conditions. It can be seenfrom such examples that the resistivity of the electrolyte is increasedin greater proportion than the voltage and that the detrimental eflectof bottle necks or other restrictions in current paths through theelectrolyte is of special importance in high voltage condensers.

It is an object of the present invention to provide maximum of anelectrode, in particular of e. g. the anode area in a given spacewithout materially increasing the equivalent series resistance or powerfactor over that of a condenser having an uncorrugated anode or an anodewith open corrugations.

This object is accomplished according to one feature of the invention bypleating the anode so that the folds forming the pleats are as sharp aspossible and so that the sides of the pleats form small acute angleswith each other. I have found that such pleating keeps the sidessubstantially straight and prevents the bowing and bottle necks abovementioned. Preferably the acute angle is not less than five degrees; or,in other words, the triangular open spaces between pleats preferablyshould have a base of at least about one-tenth the altitude or depth ofpleat.

Another feature of the invention that contrib utes to realization of theabove object relates particularly to pleated anodes for insertion in theusual round type of condenser cans of given diameter. According to such.feature, the depth of pleat is so related to the given outside diameterof the anode that maximum capacity is obtained consistent withmaintaining a given angle or triangular space between pleats.

Another object of the invention is to reduce the equivalent seriesresistance of condensers, e. g., of the types above mentioned. This isaccomplished by giving the anode a ring or annular shape and providinga, preferably, cylindrical cathode surface both inside and outsidethereof, also by insulating the electrodes so as not to obstruct thecurrent paths.

Another object is to dispose a plurality of anodes in low resistancerelation to a cathode surface.

Another and related object of the invention is to improve the mountingof anodes in condenser cans, such mountings being mechanicallyindependent of the anode lead or terminal.

A further object is to improve anode terminal connections.

Another related object is to improve the operating characteristics ofelectrolytic condensers known as the voltage-regulating type.

Other objects and advantages of the invention will be apparent from thefollowing detailed description of certain embodiments thereof, inconnection with the accompanying drawings in which, by way of examples,

Fig. 1 is a cross-section of an assembled condenser embodying theinvention.

Fig. 2 is a perspective view of a preferred form of pleated anode with aterminal connected thereto.

Fig. 3 is a perspective view of an insulator for use between anode andcathode.

Fig. 4 is a detail perspective view showing a method of forming a tabconnection.

Fig. 5 shows the preferred shape of anode pleats,

greatly magnified.

Fig. 6 is a diagrammatic showing of the resistance paths between theanode and cathode in a condenser having a bottle-necked corrugation asabove mentioned.

Fig. 7 is a graph showing the total length of anode foil for variousdepths of pleat of given included angle that can be dispcsedin a givendiameter circle or container.

Figs; 8 and 9 are cross-sections of other assembled condensers embodyingthe invention.

Fig. 10 is a partial section of a cathode support and valve forrelieving pressure from a condenser.

Fig. 11 is a partial section of an assembled condenser embodying theinvention and illustrates means for mounting the same.

Fig. 12 is a cross-sectional view of a modified form of anode mounting.

Fig. 13 is a cross-sectional view of an assembled condenser having aplurality of anodes ac cording to the invention.

Similar reference numerals indicate similar parts throughout all thefigures of the drawings.

Referring particularly to Fig. 1, the container which also may be acathode, comprises an integral mounting type can having an extrudedthreaded portion 2! and a deformable neck 22 for hermetically sealing ananode rod 23 with a soft resilient bushing 24. The bushing may be arubber stopper having a hole therethrough and is positioned on the anoderod within the deformable neck 22, which is then indented or pressedinwardly such as by rolling, spinning, staking or the like, producing aliquid tight seal. An inner container or cathode 25 which may be apressed aluminum can, extends inside the can 20 and has an outwardlyflanged top 26 which serves as a cover extending over a flange 2'! oncan 20 and is roll-seamed or pressed therewith. The joint of the twocans may be made self-venting by the inclusion of a plastic filledgasket 28 such as plasticized or wax impregnated paper or gauze. Anannular pleated anode 30 is disposed in the annular space between cans29 and 25 and is insulated therefrom by a top washer 3| of U-shapedcross-section. The anode is further insulated at its opposite end by acup-shaped washer 32 which surrounds the bottom of inner cathode 25, andby a third cup-shaped washer 33 disposed in the bottom of outer cathode20. A hole for lead 23 is provided in washer 33 in alignment with theextruded neck 22 and with the insulating bushing 24. The washers may bemade of any suitable insulating material such as perforated hard rubber,Celluloid or the like which may be pressed to shape. Alternatively, twoor more elastic bands 34 may be placed around the inner can 25 andsimilar bands 35 placed around the outside of the anode 36. In such caseflat insulating washers may be used instead of the cupshaped washers ofFig. l. The inner container 25 may be provided with projections or arolledout step 36 which engages washer 3i and further secures the anodein position. The anode terminal or lead 23 may be upset or provided witha boss as shown at 31 and riveted over anode tabs iii as indicated at33. For circuit connections, a solderable lug 4| is secured to the outerend of the anode lead 23 such as by staking.

A structure of anode 3G is more clearly exemplified in Figs. 2 and 4 inan inverted position. It is made of thin sheet metal of a width equal tothe height of the anode. To form the anode a metal sheet or strip isbent backwards and forwards upon itself 01' is passed through a pair oftoothed rollers or gears. The pleats thus formed may be made with alarge angle and then pressed together to the desired angle, or pressedto make the folds as sharp as possible and to make the pleats flat. Thenthe pleated strip may be stretched out sufficiently to give the desiredtriangular space between the pleats and the desired angle at the fold orapex as more fully described below.

For the annular form of anode illustrated in. Fig. 2, a pleated strip isbent into the form of a ring with its meeting edges joined together. Thejoining may be done by meshing the end pleats but if a more securearrangement is desired, one meeting edge may be provided with slots 42in the end fold, which slots are adapted to be engaged by tongues 43 inthe other meeting edge as shown in Fig. 4. Bending th tongues backwardupon themselves then locks the meeting edges together.

A strip or tab 4 as more clearly shown in Fig. 4, is cut from thepleated anode leaving a space 44. The tab is twisted or bent into ahorizontal position as indicated at 45, 46, and 41, thus placing the tabin a horizontal radial position extending to the center of the anode. Ifdesired, a second strip or tab is formed diametrically opposite thefirst tab as shown in Fig. 2. The tabs may be joined together andsecured to the terminal 23 such as by riveting or Welding. A suitablefiln1- forming and film-maintaining electrolyte is indicated at 58 inFig. 1 as substantially filling the space between cans 20, 25 andcovering the top of anode 36 Such an electrolyte may comprise a solutionor ester of a weak acid or weak acid salt as is well known.

Instead of using insulating washer or elastic bands as shown in Fig. 1or perforated tubular insulation as described below, insulating piecessuch as shown in Fig. 3 may be inserted between the anode and the cans.This insulating piece 5| is cut in the form of an E with spaces left at52 to provide substantially unobstructed current paths to the cathode.The material is preferably very thin sheet rubber or Celluloid and isprovided throughout with small perforations such as shown at 53. SuchE.-shaped piece may be bent into a circular arc and thus provide threeupstanding or circular strips 54 spaced about the container or anode formaintaining the anode and cathode surfaces in insulated, closely spacedrelation.

Fig. 5 shows, on enlarged scale, the preferred shape of anode pleatsforming spaces 55 each of which is an isosceles triangle, the base beingat least about one-tenth the altitude and the peak or apex 56 beingpreferably as sharp as possible. If the pleats are inch deep, forinstance, the minimum opening at the base of the triangular space 55should be about .05 inch, for the said ratio of depth to base.proportions may be used for other depths of pleat. The sides 51 of eachpleat taper uniformly from the base toward the apex and the includedangle between the sides may be about five or six degrees, which is thedesired minimum. For angles of less than five degrees or for less spaceacross the base, the condenser resistance or phase angle difference willincrease unduly because in such case the width of the current path willbe insufficient to carry all the current for the electrode area formedby the sides of the pleat, which current must pass through the base ofthe triangular body of electrolyte. I have found that the above minimumproportions prevent the creation of too high resistance in suchtriangular body. Also the straight uniformly converging sides maintainthe proportion up to the apex of the angle.

The dotted lines in Fig. 5 indicate how such a triangular pleataccording to the present invention provides straight, direct,uncongested paths from every part of the anode surfaces to the adjacentcathode surfaces 58, all said current paths being in parallel bothphysically and electrically, and having sufficiently large crosssectionso as to offer low resistances. vision of cathode surfaces on both sidesof the pleated anode make such paths available to pleats opening inopposite directions as indicated in Fig. 5. The result is a very lowresistance through the electrolyte between the entire anode and cathodesurfaces.

In contrast, Fig. 6 illustrates what happens in practice whencorrugations are formed with a relatively large radius of fold R or whenattempting to make the sides of the corrugations parallel. Theresilience of the metal in adjacent folds closes the opening of thecorrugation therebetween, at least partially, thus forming a bottle neckN of small cross-section and relatively high resistance. The individualcurrent paths C from the anode surface within the corrugation convergeat the bottle neck N so that the high resistance path P therethrough iseffectively in series with the paths C. After passing through the bottleneck the individual current paths spread out toward the cathode S. Hencethere are two factors by which such bottle necks unduly increase theequivalent series resistance and losses of a condenser, first the highseries resistance common to all the individual our- The same shape andThe prorent paths, and second, the lenghtening of such paths by forcingthem to converge and then diverge. Both of these factors are avoided inpleated anodes according to the present invention as illustrated in Fig.5.

When such a pleated anode 30 is to be bent into a ring of given outsidediameter as shown in Fig. 2, the depth of the pleats is not fixed andthey can be deep or shallow as desired. However, I have found that for agiven outside diameter of anode, foil thickness, and minimum includedangle of pleat, there is an optimum depth of pleat which will give amaximum total length of anode foil within a given outside diameter, andtherefore will give maximum capacity in the given space. If the depth isgreater than such optimum the inside circumference of the anode ringwill be smaller and the bases of the triangular spaces will be larger,hence the number of pleats in the anode ring will be decreased by bothsaid factors. On the other hand, for less than optimum depths of pleat,the loss of depth overcomes the advantage of increased number of pleat-sthat can be :placed in the anode ring.

Two examples of the length of anode foil for various depths of pleat areshown graphically in Fig. 7 and illustrate the optimum depth of pleatfor each example. Curve A is for a 1% inch diameter container in whichinch is allowed for anode insulation and clearance, thereby making thegiven outside diameter of the anode 1 inches. Curve B is for a one inchdiameter container having a inch diameter anode. In both cases the anodefoil is .005 inch thick and the pleats which open inward have theminimum triangular space proportioned as shown in Fig. 5. From thecurves, it is apparent that thirty inches of anode foil can be disposedwithin a 1 inch diameter circle if the depth of pleat is between .160and .230 inch. Similarly, from curve B it is apparent that eighteeninches of foil can be disposed in a inch diameter circle if the pleatsare about .140 inch deep.

By sacrificing an inch or so of foil length a wider range of depth ofpleat is made available, but even so the anode surface will be largerelative to the space occupied and the condenser resistance will be keptlow. Obviously, if a certain depth of pleat is desired to be madestandard for simplicity of manufacture, an average depth of pleat may bechosen which will be approximately the optimum for containers of severaldifferent diameters. Also, the advantages of the present invention maybe substantially realized even if larger pleat angles than five or sixdegrees are employed. For example, it may be desired to obtain minimumresistance and power factor with less than the maximum obtainablecapacity in a given container. In such case a larger pleat angle can bechosen so that the capacity will be maximum for that angle.

Fig. 8 shows a container 60 with a threaded mounting extrusion 6| at thebottom thereof and a bead or shoulder 62 near the top. An inner tubularcathode 63 having an outwardly flanged portion 64 and an upwardlyflanged portion 55 rests upon shoulder 62. The inner tube is suppliedwith holes 66 to allow for equalization of the pressure inside andoutside thereof. A cover 51 having an upwardly turned edge 68 and anextended portion 69 with vent holes 10, is roll-seamed with the top edgeof container 60. A diaphragm gasket 12 such as rubber, extends acrossthe top of container 60 and makes a liquid tight seal I3 as a result ofthe rollseaming operation. The diaphragm is supplied with a pin hole 74to allow the escape of gas. An anode 30 such as shown in Fig. 1 issupplied with tabs "I5 which extend radially to the center and aresecured, such as by riveting, to a riser bar 16 having a flattenedportion IT. The anode is insulated from the container 60 by insulatingcups 3|, 32 and 33, such as were described in connection with Fig. 1. Atapered rubber bushing 24 having a hole therethrough for the riser barI6 is forced into position in the neck of the container, for instance,by pulling the bushing through from the outside. A solderable terminalI8 in the form of a washer having an extruded neck is secured to theriser bar I6 as by staking at I9. Terminal I8 is supp-lied with holes 88for engaging wire terminals. The inner tube 63 may have an outwardlyflared bead 8| resting against the insulation SI for securing the anodein position. This bead may be replaced by outward indentations of theinner tube.

Fig. 9 shows a container 85 with an extruded threaded neck 86 and anoutwardly flanged top portion 81 which is roll-seamed to the edge of acover 88. A sealing gasket 89, such as rubber, is inserted between thecover and the container flange 81. An inner cathode 90 having aninwardly flanged top 9| and a hole 92 is secured to the cover such as byrivets 93. A corresponding hole 94 in the cover is in alignment withhole 92. A diaphragm gasket 85, such as rubber, is placed between flangeSI and cover 88, and is supplied with a pin hole I4 for relievingpressure within the container. Holes 66 equalize the pressure within thecontainer. The cover 88 is in dented to sink the rivets 93 below the endof the unit. In the Fig. 9 construction, an anode 9'! has circularpleats in a horizontal position. The spacing between the pleats'ispreferably at least about one-tenth the depth of the pleat for reasonsexplained above. These pleats may be obtained by rolling a metal tube,such as aluminum. Anode 91 is insulated from the inner and outer cathodesurfaces by insulating sheets 88 which may be perforated hard rubber orCelluloid bent into tubular form. The anode is supplied with tabs 99which are bent inwardly to engage the riser rod I 89 between the bossIOI and the riveted-over portion Hi2. bushing I03 insulates the boss onthe riser rod from the container. An insulating plug I54, having ashoulder I 535, is fitted within the neck 86 of the container. The riserrod I extends through centrally located holes in bushing I03 and plug IMand is secured in liquid tight seal by pressure exerted between bossIIII and the outer end of neck 35, by forcing a terminal I536 onto theriser bar Hid. An extruded portion I81 of the terminal is so shaped asto bite into the riser bar. Terminal IE is supplied with solderable lugextensions I08 for electrical connection. The inner insulating tube 98extends from the cover 88 substantially to the tabs 99 therebyinsulating the tabs from the inner container 90 and securing the anodein position. Projecting insulating tabs I89 are cut from the insulatingtubes 98 and engage the pleats of the anode for positioning the same.

Fig. 10 shows the upper end of a container 68 having a bead shoulder 62and a cooperating cover 61 which is roll-seamed to the container, as inFig. 8. The cover also has an outwardly extending portion 69 with holes75. An inner container H8 is secured to cover 5'! by a rod H2.

A rubber disc and This rod has a shoulder I I3 against which the innercontainer is secured, such as by riveting at H4. The rod extends througha hole in a rubber diaphragm II 5, the hole being slightly smaller thanthe diameter of the rod I I2 thus causing the rubber to extend upward.The rod is secured to the cover such as by riveting at I I6. Gaspressure which might generate within the container pushes the diaphragmsurrounding rod I I2 upward and the gas escapes to the atmospherethrough the holes 10. Holes 65 equalize the pressure inside and outsideof the inner container IIII.

Fig. 11 shows the lower part of an assembled condenser having an outertube I which is provided with a shoulder I2I and a roll-threaded portionI22 which seals 8. ring-type bushing I23 to an inner tube I25 which issupplied with beads I26. If desired a shoulder, such as IZI, butextending outward, may be provided on the inner tube I25 and then outertube I28 may be straight except for beads similar to I 26. An anode 81such as described in connection with Fig. 9 has leads or tabs I21extending through the ring bushing. Two tabs are shown to indicate thatthe anode may be divided within the container thus making a pluralanode, common cathode condenser. Insulation I28 such as shown in detailin Fig. 3 and bent into an arc of a circle, insulates the anode oranodes from the container. Such anodes may be secured in position asdescribed in connection with Fig. 9.

The condenser shown in Fig. 11 may be mounted by screwing it into asocket or opening adapted to engage the thread I22. Alternatively athread for mounting the condenser may be provided on the inner tube I25.By such mountings the central opening provided by the inner tube assistsin keeping the condenser cool by reason of air circulation therethrough,especially when the top of the inner tube is open as in Fig. 1.

Fig. 11 also shows an alternative mounting means in the form of a splitor divided plug I33 adapted to engage beads I26 on the inner tube. Abolt I3I having a conical head I32 disposed between the halves of plugI38 passes through a panel or member I33 upon which the condenser is tobe mounted. By tightening a nut I34 against a washer I35 and panel I33the parts of split plug I30 are spread apart so as to engage the innertube and hold the condenser securely in position.

Fig. 12 shows a container Mil having end flanges I4I for securing coversI42 and I43 such as by turning the periphery of each cover over acorresponding flange. An interposed gasket I44 may be used for sealingcover I42. A gasket for top cover I43 may be self-venting as in Fig. 1or it may be a rubber diaphragm vent M5 having a pin hole M to relievepressure in the container. In the latter case cooperating vent holes I0are provided in an extended portion I46 of the top cover. The bottomcover I42 is provided with a deformable neck I41 which is pressed orrolled into liquid tight seal with the rubberbushing I48. An aluminumWire I53 is twisted or secured into connection with a solderable lead-inwire I5I and squeezed into a liquid-tight seal within the bushing I48.An anode I 52 is mounted in the container by means of a support membersuch as an aluminum rod I53 to which the anode is secured by welding,riveting or the like. he supporting rod is held in the container byperforated aluminum discs I 54 having deformable necks I55 which arepressed into rubber bushings I56, the rod I53 being a tight fit in thebushings. The discs I54 are positioned in the container by beadindentations or shoulders I51. The aluminum wire I50 is secured to theanode support rod at its lower end, such as by wrapping, welding or thelike. Insulation I58 such as is shown in Fig. 3 may be used to insulatethe anode from the container wall and insulating washers I59 may be usedto insulate the ends of the anode from discs I54.

The condenser shown in Fig. 13 has two separate anodes and therefore isa dual capacity condenser. It comprises an outer-container cathode 60,an inner tubular cathode 63, a vented cover 61, a diaphragm gasket 12,an annular pleated anode 30, and cup-shaped insulating washers 3I, 32and 33, substantially as described in connection with Fig. 8. Inaddition the modification illustrated in Fig. 13 has a second or inneranode I60 which may be pleated or not as desired. The inner anode issupported in closely spaced, insulated relation to the inner cathode 63,for instance, by two additional cup washers I6I and I62 on opposite endsof anode I60. A head I63, or indentations in the cathode 63 help to keepanode I60 in position. Each anode is provided witha separate aluminumwire riveted or otherwise secured thereto as at I64 and I65,respectively. These wires are secured in electrical connection withsolderable lead-in wires I66 and I61, respectively, such as by welding,twisting, or the like, the connections being sealed within a bushing I60as described above in connection with Fig. 12. The extruded neck of thecontainer shown in Fig. 13 has a threaded portion 2I for mounting thecondenser and a deformable portion 22 for sealing as in Fig. 1. It isapparent in the Fig. 13 construction that the additional supportcapacity obtained from the inner anode I60 does not interfere with, ordetract from, the capacity obtained from the outer anode 30. It is alsoapparent that both the inner and outer surface of the tubular cathode 63and substantially all of the space within container 60 are utilizedeffectively. v

In the condenser assemblies described above by way of example the anodesare supported independently of their riser rods or lead-in connections.The flexibility of the anode connecting tubes or wires facilitatesassembly and prevents transmission of strains from the terminal to theanodes.

The general characteristics of electrolytic condensers and the materialsused therein are so well known that description thereof in connectionwith the condensers shown in the drawings appears to be unnecessary. Itmay be mentioned however that if a liquid or wet electrolyte is used itis run into the container to a predetermined level with the anode inposition, then the inner cathode is put in place thus forcing theelectrolyte up to the desired level over the anode as indicated in Fig.1, for instance about inch above the top of the anode. The top of thecondenser is then roll-seamed and sealed.

The anode may be made of any film-forming metal but aluminum isgenerally preferred and used. The container and/or other cathodesurfaces are preferably non-film-forming, but instead of using anon-film-forming metal therefor, aluminum may be used and may be platedwith chromium on the surfaces which make contact with the electrolyte.The inner cathodes shown in Figs. 8, 9, 10 and 13 need not bemeincreasing the resilience of the folds.

chanically strong, so they may be made of very thin metal and in somecases of foil.

The foil used for the anode 24 preferably has its effective areaincreased 300 or 400 percent by etching the foil before or afterpleating, preferably before. This may be done by chemical, electrolytic,or mechanical processes, or by a combination thereof. For instance, astrip of aluminum foil for the anode may be passed through a solution ofa halogen salt and a voltage impressed between the aluminum and anotherelectrode, the solution having suflicient resistance to cause breakdownof the dissolved halogen salt into its component parts wherein thehalogen will attack the aluminum forming microscopic peaks and craters,thus increasing the surface area of the foil.

The electrolytic film which acts as the dielectrio in the condensersdescribed herein may be formed on the anode by well known methods afterit is etched, pleated and assembled. However, I prefer, e. g., thefollowing order of process steps for preparing the anode.

1. Cleaning and etching of a straight aluminum foil in a continuousprocess.

2. A preliminary film formation on the etched foil, also continuous.

3. Pleating the said foil and cutting it into desired lengths.

4. Fabrication of the pleated foil to the desired anode shape andassembly with a terminal.

5. A second film-forming in an aqueous solution containing approximately100 grams of boric acid and two grams of borax per liter.

6. Assembly in a container with the operating electrolyte, the latterhaving a temperature of about 80 C.

7. Immediate ageing of the assembled condenser while hot by applying aD. C. voltage equal to the operating voltage, the anode being positive.

Relative to the second above step, I have found that preforming stiffensthe foil so that the sides of the pleats are stiffer but withoutmaterially Thus the pleating and fabrication are more easily performedand the anode is less apt to be distorted from the desired shape. Thepresence of the preformed film reduces the coefficient of friction andthus aids the pleating operation, and in addition reduces the timerequired to form the final film.

Relative to the fifth above step, the forming voltage for the usual typeof condenser is preferably 10% above its given operating voltage.However for the voltage regulating type of condenser the forming voltageshould be substantially equal to the given operating voltage. The lattertype should have a low leakage current at the operating voltage and arapidly increasing leakage current above the operating voltage. Whensuch a condenser is used in connection with vacuum tubes supplied by arectifier (as in the usual radio receiver) the condenser leakage currentputs a load on the rectifier and prevents the rectifier voltage fromrising to dangerous values while the vacuum tubes are heat ing up orotherwise not drawing their nor plate current. After normal plate cu tload is drawn by the vacuum tubes the rectifier voltage becomes normaland t condenser l a a is malL In order to perform satisfactorily such aVoltage egulating function, the equivalent Series resistance of thecondenser must be Small ecause such resistance must be overcome by theleakage current. A high resistance condenser would have a high internalvoltage drop and therefore could not reduce the rectifier voltage. Thecondensers described herein are especially suitable for voltageregulation because they have very loW resistance.

The equivalent series resistance is further decreased by reason of theclose spacing of the cathode both inside and outside the pleated anodethereby making the current path through the electrolyte short and oflarge area, and also of low contact resistance between the cathode andthe electrolyte. It is understood of course that the height of the anodeand cathode surfaces may be chosen as desired, the capacity of thecondenser being substantially directly proportional to the height of theanode, other factors being the same.

It is understood that all features of the invention which were indicatedas related ones may be applied and used individually and independentlyfrom each other, and that any and all details described hereinbefore maybe applied and used with condenser structures other than shownhereinbefore by way of example only.

I claim:

1. A container for an electrolytic condenser comprising two aluminumcans, one of said cans having less diameter and length than the otherand coaxially disposed therein, a pleated annular shaped anode disposedbetween said cans, the volume enclosed by the surfaces circumscribingand inscribing said anode being approximately one to one and a halftimes the volume enclosed by said inscribing surface, a flange closingthe annular space between said cans at one end thereof, and a ventinggasket forming part of said closure; said cans being individually closedat the other end thereof.

2. An electrolytic condenser comp-rising a substantially can-shapedcylindrical container, a pleated anode of substantially annularconfiguration arranged within and in spaced relation to the cylindricalwall of said container, a substantially cylindrical electrode inside andin spaced relation to said pleated anode, said electrode connected withsaid container, another pleated anode of substantially annularconfiguration arranged within and in spaced relation to said cylindricalelectrode, and an electrolyte contacting said pleated anodes, said walland said electrode.

3. An electrolytic condenser comprising a substantially can-shapedcylindrical container, a pleated anode of substantially annularconfiguration arranged within and in spaced relation to the cylindricalwall of said container, a substantially cylindrical electrode inside andin spaced relation to said pleated anode, said electrode connected withsaid container, another pleated anode of substantially annularconfiguration arranged within and in spaced relation to said electrode,and an electrolyte contacting said pleated anodes, said wall andelectrode, the volume between two substantially cylindrical surfacescircumscribing and inscribing said first mentioned pleated electrodeapproximating from one to one and a half times the volume enclosed bysaid inscribing surface.

4. An electrolytic condenser comprising a substantially cylindricalcontainer, an annular pleated anode arranged within and in spacedrelation to said container, the inside apices of the pleats of saidanode inscribing a substantially cylindrical volume approximatingone-half to threequarters of the annular volume occupied by said anode,a substantially cylindrical electrode arranged inside and in spacedrelation to said pleated anode, said latter electrode connected withsaid container and provided with communicating passages, another anodearranged within said latter electrode in spaced relation thereto,terminals connected with said anodes and insulatingly extending throughsaid container, and an electrolyte within said container contacting it,said electrode and anodes.

5. An electrolytic condenser comprising a container having inner andouter walls forming an annular space therebetween, an electrolytesubstantially filling said space, an annular shaped anode immersed insaid electrolyte, rings of insulation around the inner metal wall andother rings of insulation around the outside of said anode, andinsulating washers disposed between the ends of said metal walls.

6. An electrolytic condenser comprising a cylindrical cathode containerand a further cylindrical cathode of lesser diameter than saidcontainer, one end of said cylindrical cathode being supported from oneend of said container to form a pair of communicating annular andcylindrical spaces between said container and cathode and inside saidcathode, respectively, an annular shaped anode disposed within saidannular space in spaced relationship to the walls of said container andcathode to form a first condenser unit, means insulatingly supportingsaid anode from said container, a further anode disposed in spaced relationship with the inner surface of said cathode to form a secondcondenser unit therewith, means insulatingly supporting said secondanode from said container, and an electrolyte within said annular andcylindrical spaces common to both said condenser units.

WILLIAM DUBILIER.

